Conventional lumber stackers have been refined over the years so as to operate quite adequately under basic situations, but are found to be inadequate when it comes to stacking at higher speeds and are not very versatile. The problems that are encountered are mostly in the feeding, separating and subsequent stacking of the tiers of rough sawn lumber into an even stack. There are fewer problems encountered when dealing with lumber that has been planed which is uniform in width and height, but when the lumber being stacked is of varying widths and slightly varying in thickness and bowed (as may be more predominant in modern curve sawing mills), cupped or crooked, it becomes increasingly difficult to create acceptable stacks with known stackers of the general type. There have been some attempts at solving these problems in the past, but these devices are usually limited in their success when the lumber being stacked is not uniform in size and shape, and when the stacking speeds are increased.
An example of an improved lumber or board stacker is U.S. Pat. No 4,892,458 which issued to Prouix on Jan. 9, 1990. Although this system is somewhat successful at delivering lumber at higher speeds, it is complex and requires a large area (which is not always available), and it is not designed for stacking rough sawn lumber.
Applicant is also aware of U.S. Pat. No. 2,861,702 issued to Mason on Nov. 25, 1958. This device considers the need to stack slight varying lumber widths (rough lumber) and yet obtain a consistent width of package. This device is not however capable of satisfactorily high speed stacking and is not capable of stacking variable widths of stacks.
Applicant is also aware of U.S. Pat. No. 2,730,247 issued to Lawson on Jan. 10, 1956. This device considers the need to stack varying lumber widths (rough lumber) and yet obtain a consistent width of package. Again, the Lawson device would not be capable of satisfactorily stacking at high speeds and is not capable of stacking variable widths of stacks, and would require quite a large area in the sawmill.